High speed printing machines have been developed in recent years for printing data on computer paper, business forms, labels, tickets and the like. The paper supplied to such printers is provided in webs of indeterminate length formed with longitudinally spaced, transversely oriented perforations. The paper is fed at high speeds from the web to the printer which prints the desired information on the individual sheets formed between adjacent perforations, and then discharges the printed sheets for further handling. In order to convert the continuous length of paper from the printer into a form which can be handled and shipped, the paper must be folded along its perforations as it is discharged from the printer. One type of folding apparatus intended for use with high speed printers is a spiral, zig-zag folder.
Spiral zig-zag folders include a series of rollers which receive the continuous length of paper from the web and guide it to a reciprocating swing chute mechanism. The swing chute is driven forwardly and rearwardly relative to the frame of the folder through a distance or throw which is proportional to the distance between the longitudinally spaced, transverse perforations in the paper. At both the forward and rearward limit of the throw of the swing chute, a set of beaters or knock-down fingers engages the paper in the area of its perforations and forces it into contact with one or more rotating spirals. These spirals resemble a screw having threads which are spaced progressively closer together from top to bottom. The paper is forced by the knock-down fingers into the wider threads at the top portion of the spirals, and, as the spirals rotate, the paper is transferred to progressively narrower threads thus forming a crease in the paper along its perforations. The resulting zig-zag folded sheets are then discharged from the spirals onto a ramp or shelf for stacking.
In addition to operating at high speeds, present day printers are also capable of accommodating different webs of paper, each having different widths and/or different spacing between the transverse perforations. Narrow sheet material, such as labels, tickets and similar items, may have a width as small as 11/2 inches. While printers are capable of handling narrow stock, it has been found that spiral, zig-zag folders of the type described above are ineffective in folding stock less than about 41/2 inches in width. Such difficulty in handling narrow stock can be attributed to the imposition of side-to-side vectors or forces on the sheet material by the rotating spirals as the crease is formed along the perforations between adjacent sheets. As noted above, the sheet material is directed by the knock-down fingers to the spirals which rotate in order to form the crease along the perforations. In the course of rotating, the spirals impart side-to-side vectors or forces to the sheet material tending to move the sheet material in a side-to-side direction with respect to the frame of the folder. This can cause the sheet material to disengage the spirals and/or create alignment problems which results in either an incomplete fold along the transverse perforations or jamming of the folder.